A pouch electric cell has a battery cell therein, and a polymer wrapping corresponding to a pouch is provided to surround the battery cell.
With reference to FIG. 1 showing a perspective view of a pouch electric cell and FIG. 2 showing a sectional view taken along the line A-A′ of FIG. 1, a pouch electric cell 100 includes an electrode 110, a pouch 120 and a battery cell 130.
To make such a pouch electric cell 100, as shown in FIG. 3, pouch raw materials of a predetermined size are adhered to the battery cell 130 from upper and lower portions thereof such that a pouch surrounds the battery cell 130.
This pouch 120 protects the battery cell 130, and the pouch 120 is made of aluminum foil to improve electric and chemical properties and heatproof property of the battery cell 130. Also, in order to ensure insulation of the battery cell 130 against the exterior, the aluminum foil is coated with an insulating material such as polyethylene terephthalate (PET) resin or nylon resin.
In case the pouch is composed of upper and lower pouch portions adhered to each other as shown in FIG. 3, cast polypropylene (CPP) or polypropylene (PP) may be used for adhesion between them. In this case, a sealing surface where the pouch 120 is adhered may be configured with an insulating layer 121, an aluminum layer 123 and an adhering layer 125 as shown in FIG. 4.
If the inner structure of the pouch of the pouch electric cell 100 is broken or damaged due to an external physical impact and thus the pouch electric cell 100 loses its insulation, the battery cell does not keep a normal voltage but causes low voltage, which may also cause swelling of an interior battery cell.
This problem may causes consecutive problems such as explosion of the battery cell, which is crucial to users or equipped devices, so it is required to thoroughly check insulation of the pouch electric cell 100 and thus fundamentally eliminate any defect.
Seeing a frequently used method for checking insulation of a pouch electric cell, as shown in FIG. 5, probes 502 are contacted respectively to an electrode 110 of the pouch electric cell 100 and an aluminum layer 123 at a side of the pouch 120, and then resistance between the contacted probes is measured using a measuring device 500 to check insulation.
In this method, the probe should be contacted to the aluminum layer 123 so as to measure insulation, but the probe 502 and the aluminum layer 123 make point contact, which does not ensure high reliability. In addition, if a force is applied to make a physical contact between the probe 502 and the aluminum layer 123, an outer periphery of the pouch may not endure the applied force due to its material but be easily deformed. Thus, the physical contact for electric connection between the probe 502 and the aluminum layer 123 may not be easily maintained, thereby giving difficulty to the checking process.
Due to the above circumstances, the reliability of the insulation checking for a pouch electric cell is very deteriorated though it consumes much time. In addition, it is difficult to eliminate an inferior battery cell, and the appearance of the pouch is still easily broken. Also, this conventional checking method becomes a serous obstacle in automating the insulation checking process for a pouch electric cell.